Radio frequency transformer for induction heating installation

ABSTRACT

In a radio frequency transformer for an induction heating device including a primary winding and a secondary winding defining a central chamber there is provided a core structure including a closed, non-magnetic housing having an outer wall generally matching the inner surface of the chamber, a plurality of high permeability elements secured within the housing and adjacent the outer walls thereof, and means for circulating a coolant through the housing and in heat transfer relationship with the elements.

United States Patent [1 1 Kec 1 1 June 19, 1973 RADIO FREQUENCY TRANSFORMER FOR INDUCTION HEATING INSTALLATION [75] Inventor: William J. Kec, Chippewa Lake,

Ohio

[73} Assignee: Park-Ohio Industries, Inc., Cleveland.Ohio

[22] Filed: Jan. 10, I972 [21] Appl. No.: 216,682

336/234 [51] Int. Cl. 1105b 5/06 [58] Field of Search 219/10.75, 10.77,

[56] References Cited UNlTED STATES PATENTS 2,856,499 10/1958 Stanton et al 219/10.75 3,377,565 4/1968 Denner 219/10.75 X

2,179,661 11/1939 Jones 336/234 X 3,021,413 2/1962 Blok 219/10 75 2,962,679 11/1960 Stratton 336/234 X FOREIGN PATENTS OR APPLICATIONS 1,098,613 8/1955 France ..219/10.75 1,096,926 6/1955 France ..219/10.75

Primary Examiner-J. V. Truhe Assistant Examiner-B. A. Reynolds Attorney-James H. Tilberry, Alfred C. Body and Robert V. Vickers [57] ABSTRACT ln :1 radio frequency transformer for an induction heating device including a primary winding and a secondary winding defining a central chamber there is provided a core structure including a closed, non-magnetic housing having an outer wall generally matching the inner surface of the chamber, a plurality of high permeability elements secured within the housing and adjacent the outer walls thereof, and means for circulating a coolant through the housing and in heat transfer relationship with the elements,

13 Claims, 4 Drawing Figures Patented June 19, 1973 3,740,516

3 Sheets-Sheet 1 Patented June 19, 1973 5 Sheets-Sheet 2 FIG. 3

Patented June 19, 1973 Z Sheets-Sheet (5 OS CILLATOR RADIO FREQUENCY TRANSFORMER FOR INDUCTION HEATING INSTALLATION This invention relates to the art of induction heating and more particularly to an improved radio frequency transformer for use in an induction heating installation.

The invention is particularly applicable for a transformer used in energizing a number of individual inductors for inductively heating the valve seats of an engine head, and it will be described with particular reference thereto; however, it must be appreciated that the invention has broader applications and may be used in a variety of radio frequency transformers for induction heating installations.

With the change to the use of low lead gasolines in internal combustion engines, it has become somewhat common practice to inductively heat and quench harden the exhaust port valve seats in the engine head of the engine. The equipment adopted for performing this hardening operation is disclosed in prior patent application Ser. No. 151,493, filed June 9, 1971, and includes a radio frequency transformer having a primary winding connected to the tank circuit of an oscillator and a secondary winding connected across a number of small transformers arranged in a series circuitfThe small transformers are each individually connected to an inductor which is movable to a position adjacent the conical seat of an exhaust port. When the radio frequency transformer is energized, the several individual transformers energize the inductors to heat inductively the respective valve seats. Thereafter, valve seats are air quenched to harden the same. The present invention relates to an improvement in the radio frequency transformer of the apparatus as disclosed in the previous pending patent application.

The radio frequency transformer includes a multiturn primary and a single turn secondary with the primary positioned within the secondary. The output leads of the single turn secondary are connected across the respective inductor transformers. With this arrangement, certain difficulty was experienced in developing sufficient power at the respective inductors. This increased the required heating cycle and reduced the total electrical efficiency from the oscillator to the inductor. To decrease the time required to heat the valve seats it was suggested to apply a higher voltage to the primary of the main radio frequency transformer; however, this was not economically feasible. 1n the prior radio frequency transformer it was found that there was a need to adjust the energy output of the radio frequency transformer as conditions varied in the load. This adjustment was necessary after the transformer was mounted on the equipment and during start-up of the installation. There was no convenient way for adjusting the power output of the transformer after the transformer had been so assembled.

All of these disadvantages have been overcome by the present invention which relates to an improvement in a radio frequency transformer of the type used for an induction heating installation. In accordance with this improvement, the radio frequency transformer is provided with an internal core within the central passage of the transformer, which core includes a layer of high permeability material adjacent the inside of the transformer so that an increased efficiency is created between the secondary and primary of the transformer. In the past, radio frequency transformers of the type adapted to operate induction heating installations in excess of 15,000 cycles per second have not included high permeability material because of the hysteresis loss in such material during high frequency operation caused undue heating. However, it has been found that with the present transformer, having an internal multiturn primary and an external single turn secondary, the hysteresis losses in the externally positioned high permeability material are not excessive. This high permeability material does contribute to the more efficient coupling of the primary and secondary winding, both of which are spaced outwardly from the high permeability material of the core structure.

In accordance with another aspect of the present invention there is provided an improvement in a radio frequency transformer, which improvement includes a core structure having a closed, non-magnetic, electrically non-conductive housing with an outer wall generally matching the internal configuration of the transformer, a plurality of high permeability elements secured within the housing and adjacent the outer wall of the housing, and means for circulating a coolant through the housing and in heat transfer relationship with the elements. By this arrangement, the heat caused by the hysteresis losses within the high permeability material is dissipated and does not cause overheating of the elements. It is noted that the high permeability material within the transformer is not magnetically coupled to both the primary and secondary as in a normal transformer of a lower frequency type. In addition, it is well known that radio frequency transformers generally do not include core material because of the hysteresis loss. Consequently, the use of a core material in a radio frequency transformer and the use of this core material outside the air gap between the primary and secondary windings of the transformer does not follow normal practice in constructing radio frequency transformers. This arrangement has proven beneficial in increasing the efficiency of a radio frequency transformer used for powering a plurality of inductor transformers in a valve seat induction heating installation.

In accordance with still a further aspect of the present invention, the core structure mentioned above is adjusted in a direction axial of the windings of the radio frequency transformer to adjust the energy output of the transformer. This arrangement provides a convenient manner for adjusting the energy applied to the several individual inductor transformers in the induc tion heating installation for individual exhaust valve seats. In this manner, the optimum energy output for the transformer can be obtained after the equipment has been assembled at the using site without changing the transformer itself or modifying the optimum input to the transformer.

The primary object of the present invention is the provision of a radio frequency transformer of the type used in induction heating installations, which transformer has an improved efficiency.

Another object of the present invention is the provision of a radio frequency transformer for induction heating installation, which transformer includes a plurality of high permeability elements outside the windings of the transformer for improving the efficiency of the transformer.

Yet another object of the present invention is the provision of a radio frequency transformer of the type used for induction heating, which transformer includes means for adjusting the coupling between telescoped, concentric primary and secondary windings.

These and other objects and advantages will become apparent from the following description used in connection with the accompanying drawings in which:

FIG. 1 is a top plan view illustrating, somewhat schematically, the preferred embodiment of the present invention;

FIG. 2 is a side elevational view showing the preferred embodiment of the present invention;

FIG. 3 is a partial cross-sectional view taken generally along line 33 of FIG. 1; and,

FIG. 4 is a partial cross-sectional view taken generally along line 4-4 of FIG. 1.

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, the figures show an induction heating installation A used for inductively heating separate, spaced exhaust valve seats in the engine head of an internal combustion engine and including a transformer B and a load circuit C. The load circuit employs output leads l0, 12 connected across a number of inductor transformers 14 each having a secondary connected to an inductor 16. The inductors are used, in the normal manner, for inductively heating the valve seats in the engine head as shown in prior application Ser. No. ll,493, filed June 9, 1971.

Referring now to the transformer B, there is included a multi-turn primary winding 20 and a single turn secondary winding 22 electrically attached to connectors 24, 26 for energizing the load circuit C. Referring in more detail to the primary winding 20, input terminals 30, 32 are adapted to be connected to the tank circuit of an oscillator, schematically illustrated as oscillator 33 in FIG. 2. The winding 20 is encapsulated within a material 34 which is non-magnetic and electrically nonconductive so that it has no electrical effect upon the transformer. The generally cylindrical primary 20 has an inner periphery 36 and the insulating material 34 defines an inner chamber surrounded by this periphery. The multi-turn primary includes an upper end 42 electrically connected with the terminal 32 and a lower end 44 connected to the terminal 30. This provides an electrical circuit through the multi-turn primary winding so that the winding is part of the tank circuit of oscillator 33.

Referring now to the secondary winding 22, this winding includes a single sheet 48 having spaced edges 50, 52 electrically attached to connectors 24, 26, in a manner to be described later. The winding 22 is generally cylindrical, as is the primary winding, and includes a ccentral axis x which basically coincides with the central axis of the primary winding in the mounted position as shown in FIGS. 1 and 3. The outer periphery 54 is defined by the outside surface of the single sheet 48 which is held in position with respect to the primary winding 20 to define air gap 56. It is appreciated that the air gap is filled with the insulation material 34; however, this material is non-magnetic and not electrically conductive so it has a permeability of approximately 1.0 and serves as a normal air gap through which the primary is magnetically coupled to the secondary.

Referring now in more detail to the connectors 24, 26 the secondary sheet 48 is brazed at edges 50, 52 with two spaced, elongated coupling bars 60, 62 separated by a strip of insulation material 64 and held in the spaced position by insulated straps 70, 72 secured across the respective ends of the coupling bars by a plurality of bolts 74. Bus bars 80, 82 forming the leads 10, 12 in the load circuit are separated by an insulation strip 84 and are held onto the coupling bars 60, 62 by a plurality of spaced bolts 86. In this manner, the edges 50, 52 are electrically isolated from each other and form the output section for the secondary winding 22 while the bus bars 80, 82 are connected into the load circuit for energizing the transformers l4 and, in turn, the inductors 16 when the inductors are positioned adjacent the exhaust valve seats of the engine head. Although it forms no part of the present invention, the transformer B is provided with appropriate coolant systems. For cooling purposes, primary 20 is formed from a hollow conductor and a coolant is introduced into terminal 32, then flows through the primary winding and out terminal 30. To cool the secondary winding 22, there is provided an inlet for directing coolant through conduits 92, 94, 96, 98 and 100, respectively, to an outlet 102. The conduits 92, 96 and 100 are secured onto and extend around the sheet 48 while the conduits 94 and 98 extend along the coupling bars 60, 62 for the purpose of cooling the same.

As so far described, the transformer B is constructed in accordance with the common practice for a radio frequency oscillator functioning above approximately 15,000 cycles per second. It is noted that there is an air gap between the primary and secondary windings and magnetic coupling is effected through this air gap to energize the secondary sheet winding. In accordance with the present invention, there is provided a core D positioned within the inner chamber 40 and adjacent the inner periphery 36 of primary winding 20. Basically, this core includes a plurality of elongated high permeability elements positioned in parallel relationship to the axes of the primary and secondary windings and adjacent the periphery 36. To accomplish this function, a variety of structures are possible; however, in accordance with the preferred embodiment of the present invention, as best shown in FIGS. 1 and 4, the core D includes a housing formed from a plastic material, such as plexiglass or fiber glass. The housing includes an outer wall 112 having a generally cylindrical portion 112a matching the periphery 36 of the primary winding 20, and a generally flat portion ll2b providing clearance for the terminals 30, 32. Also included in the plastic housing is a top end plate 114 and a bottom end plate 116 which combine with the outer wall to define an inner, closed chamber 118. The chamber 40 formed by the insulating material 34 has an internal shape generally matching the shape of outer wall 112 of housing 110 and includes a generally cylindrical portion 120 and a generally flat portion 122. The end plate 114 has a downwardly extending rib and the opposite end plate 116 has an upwardly extending rib 132. These ribs combine to define an upper recess 134 and a lower recess 136 into which a plurality of elongated ferrite rods 140 are positioned. If there is space between adjacent rods, this can be filled by any appropriate material, preferably a non-magnetic material to secure the elements in a generally fixed condition. The use of the ferrite rods outside the air gap 56 has been found to increase the efficiency of the coupling between the primary and secondary windings of the radio frequency transformer B. These ferrite rods form flux concentrators maintaining a high flux field in the coupling air gap without providing the high permeability within the air gap itself which would be detrimental because of hys teresis losses. In addition, ferrite material within the air gap would preclude direct magnetic coupling between the transformer winding. Ferrite material in the air gap, which has a relatively small dimension in a radial direction, would preclude efficient cooling of the material to dissipate any energy caused by hysteresis losses within the material. In accordance with the present invention, by using the high permeability, ferrite core material adjacent the inner periphery of the primary winding 20, there can be efficient and quite simple cooling arrangement for the ferrite core elements. The chamber 118 is a cooling chamber which is directly exposed to the major length of the ferrite rods 140, as best shown in FIG. 4. A coolant inlet 150 is communicated with chamber 118 and directs a coolant into the chamber where it comes into direct contact with the axially extending ferrite rods 140. An outlet 152 is provided to direct the coolant from the chamber 118. In accordance with this illustrated embodiment, the deflector tube 154 is secured below the outlet 152 so that the coolant flowing into the chamber 118 must take a path substantially as defined by the arrows shown in FIG. 4 from the inlet 150 into the tube 154 and then from the tube out the outlet 152. This provides an efficient circulation of the coolant within the chamber 118. To drain the chamber, there is provided a drain outlet 160 in the lower end plate 116. Other arrangements could be provided for draining the coolant from the housing 110.

In accordance with one aspect of the invention, the core D may be adjusted in an axial direction within the chamber 40 to adjust the magnetic coupling between the primary and secondary windings. This adjusts the output of the secondary winding in a convenient manner after the radio frequency transformer has been installed. In accordance with the preferred embodiment of the present invention, a non-magnetic, electrically non-conductive block 170 is positioned between the lower end plate 116 and a fixed support structure 172, which may be the supporting structure for the transformer B. By changing the thickness of block 170, the axial position of the core D can be changed within the chamber 40. In this manner, a different portion of the axial length of the transfer is affected by the rods 140 and an adjustable inductance is provided for the transformer for the purpose previously described.

Having thus described my invention, I claim:

1. In an induction heating device including at least one inductor adapted to heat inductively a workpiece magnetically coupled thereto, a radio-frequency transformer having a secondary winding coupled to said inductor and a primary winding adapted to be coupled to a source of radio frequency energy, said secondary winding and said primary winding being generally cylindrical, having respective central axes, and being telescopically and generally coaxially positioned with respect to each other to define a central open chamber inside both of said windings and having an outer boundary generally defined by one of said windings, the improvement comprising: an axially movable core structure positioned in said central chamber, said core structure comprising a closed housing formed from nonmagnet, non-conductive material with an outer wall generally matching said boundary and an internal cavity, a layer of high permeability material adjacent a major portion of said outer wall, said layer defining a core chamber and means for circulating a coolant through said core chamber and into contact with said layer.

2. The improvement as defined in claim 1 wherein said layer comprises a plurality of separate, elongated rod-like elements extending generally axially of said windings.

3. The improvement as defined in claim 2 including means for varying the effective axial length of said elements in said chamber to vary the output energy induced into said secondary winding.

4. The improvement as defined in claim 3 wherein said varying means includes means for moving said elements in a direction axially of said windings.

5. In a radio-frequency transformer for an induction heating device including a primary winding and a secondary winding, said windings each being generally cylindrical and having a central axis, and means for fixedly securing said windings in a telescopical, coaxial relationship, said transformer having a central opening inside both of said windings and having an outer boundary generally defined by one of said windings, the improvement comprising: a core structure mounted within said chamber, said core structure including a closed, non-magnetic housing having an outer wall generally matching said boundary and spaced therefrom, a layer of high permeability material adjacent a major portion of said outer wall and in the form of a plurality of high permeability elements secured within said housing and adjacent said outer wall, and means for circulating a coolant through said housing and in heat transfer relationship with said elements.

6. The improvement as defined in claim 5 wherein said elements are elongated and extend in a direction generally axially of said windings.

7. The improvement as defined in claim 6 wherein said housing includes means engaging the respective ends of said elements for securing said elements adjacent said outer walls of said housing.

8. The improvement as defined in claim 7 including means for adjusting said housing in a direction axially of said windings whereby the magnetic coupling between said windings is varied.

9. The improvement as defined in claim 7 wherein said housing has axially spaced closure plates and said securing means includes means on said plates for engaging said respective ends of said elements.

10. The improvement as defined in claim 9 wherein said engaging means are inwardly extending flanges on said plates.

11. The improvement as defined in claim 5 including means for adjusting said housing in a direction axially of said windings whereby the magnetic coupling between said windings is varied.

12. The improvement as defined in claim 5 including means for draining coolant from said closed housing.

13. A radio-frequency transformer for use in an induction heating installation, said transformer including a generally cylindrical, multi-turn primary winding having a central axis and a generally cylindrical inner periphery; a generally cylindrical, single turn secondary winding having a central axis and a generally cylindrical outer periphery; said primary winding being smaller than said secondary winding and being telescopically received within said secondary winding in a coaxial, radially spaced position to define an air gap between said primary and secondary windings, a plurality of elonfor circulating a coolant in said housing and around gated high permeability elements positioned parallel to said elements; and, means for adjusting the axial posithe axes of said windings and adjacent one of said petion of said housing within said windings.

ripheries, a housing surrounding said elements; means 

1. In an induction heating device including at least one inductor adapted to heat inductively a workpiece magnetically coupled thereto, a radio-frequency transformer having a secondary winding coupled to said inductor and a primary winding adapted to be coupled to a source of radio frequency energy, said secondary winding and said primary winding being generally cylindrical, having respective central axes, and being telescopically and generally coaxially positioned with respect to each other to define a central open chamber inside both of said windings and having an outer boundary generally defined by one of said windings, the improvement comprising: an axially movable core structure positioned in said central chamber, said core structure comprising a closed housing formed from non-magnet, nonconductive material with an outer wall generally matching said boundary and an internal cavity, a layer of high permeability material adjacent a major portion of said outer wall, said layer defining a core chamber and means for circulating a coolant through said core chamber and into contact with said layer.
 2. The improvement as defined in claim 1 wherein said layer comprises a plurality of separate, elongated rod-like elements extending generally axially of said windings.
 3. The improvement as defined in claim 2 including means for varying the effective axial length of said elements in said chamber to vary the output energy induced into said secondary winding.
 4. The improvement as defined in claim 3 wherein said varying means includes means for moving said elements in a direction axially of said windings.
 5. In a radio-frequency transformer for an induction heating device including a primary winding and a secondary winding, said windings each being generally cylindrical and having a central axis, and means for fixedly securing said windings in a telescopical, coaxial relationship, said transformer having a central opening inside both of said windings and having an outer boundary generally defined by one of said windings, the improvement comprising: a core structure mounted within said chamber, said core structure including a closed, non-magnetic housing haVing an outer wall generally matching said boundary and spaced therefrom, a layer of high permeability material adjacent a major portion of said outer wall and in the form of a plurality of high permeability elements secured within said housing and adjacent said outer wall, and means for circulating a coolant through said housing and in heat transfer relationship with said elements.
 6. The improvement as defined in claim 5 wherein said elements are elongated and extend in a direction generally axially of said windings.
 7. The improvement as defined in claim 6 wherein said housing includes means engaging the respective ends of said elements for securing said elements adjacent said outer walls of said housing.
 8. The improvement as defined in claim 7 including means for adjusting said housing in a direction axially of said windings whereby the magnetic coupling between said windings is varied.
 9. The improvement as defined in claim 7 wherein said housing has axially spaced closure plates and said securing means includes means on said plates for engaging said respective ends of said elements.
 10. The improvement as defined in claim 9 wherein said engaging means are inwardly extending flanges on said plates.
 11. The improvement as defined in claim 5 including means for adjusting said housing in a direction axially of said windings whereby the magnetic coupling between said windings is varied.
 12. The improvement as defined in claim 5 including means for draining coolant from said closed housing.
 13. A radio-frequency transformer for use in an induction heating installation, said transformer including a generally cylindrical, multi-turn primary winding having a central axis and a generally cylindrical inner periphery; a generally cylindrical, single turn secondary winding having a central axis and a generally cylindrical outer periphery; said primary winding being smaller than said secondary winding and being telescopically received within said secondary winding in a coaxial, radially spaced position to define an air gap between said primary and secondary windings, a plurality of elongated high permeability elements positioned parallel to the axes of said windings and adjacent one of said peripheries, a housing surrounding said elements; means for circulating a coolant in said housing and around said elements; and, means for adjusting the axial position of said housing within said windings. 